Method of, and Apparatus for, Measuring the Quality of a Surface of a Substrate

Abstract

A method of measuring the quality of a surface of a substrate is described. The method includes the steps of obtaining a digital image of a portion of a surface of the substrate using an image obtaining apparatus; and measuring one or more physical characteristics of the obtained digital image so as to provide an indication of the quality of the surface of the substrate.

1 . A method of measuring the quality of a surface of a substrate, including the steps of: —
 obtaining a digital image of a portion of a surface of the substrate using an image obtaining apparatus; and measuring one or more physical characteristics of the obtained digital image so as to provide an indication of the quality of the surface of the substrate.   
   
   
       2 . A method according to  claim 1  including the step of illuminating, at an angle to a general plane of the substrate, the portion of the surface of the substrate prior to the digital image being obtained. 
   
   
       3 . A method according to  claim 1  wherein the obtained digital image includes a plurality of pixels and the method includes measuring, for a test area of pixels within the obtained digital image, a physical characteristic of each pixel and comparing the measured physical characteristic of each pixel within the test area with the measured physical characteristic of an adjacent pixel. 
   
   
       4 . A method according to  claim 1  wherein the physical characteristic measured is a luminance of each pixel. 
   
   
       5 . A method according to  claim 1  including the step of comparing the measured physical characteristic of each pixel within the test area with the measured physical characteristic of two or more adjacent pixels. 
   
   
       6 . A method according to  claim 1  wherein the test area of pixels within the obtained digital image includes a plurality of pixels in rows and columns and the method includes comparing the measured physical characteristic of each pixel within the test area with the measured physical characteristic of a first adjacent pixel located in the same row and with the measured physical characteristic of a second adjacent pixel located in the same column. 
   
   
       7 . A method according to  claim 6  including comparing the measured physical characteristic of each pixel within the test area with the measured physical characteristic of an adjacent pixel located in an adjacent row or column. 
   
   
       8 . A method according to  claim 1  include measuring for a test area of pixels within the obtained digital image, a physical characteristic of a group of adjacent pixels and comparing the measured physical characteristic of that group of pixels with the measured physical characteristic of an adjacent group of pixels. 
   
   
       9 . A method according to  claim 8  wherein the measured physical characteristic is an average luminance of each group of adjacent pixels. 
   
   
       10 . A method according to  claim 1  wherein, where the obtained digital image is a colour digital image, the method includes the step of converting the colour digital image to a gray-scale digital image before a physical characteristic of each pixel of the digital image is measured. 
   
   
       11 . A method according to  claim 10  including the step of measuring for the test area of the digital image the average pixel luminance value and the standard deviation of the luminance values for all of the pixels in the test area. 
   
   
       12 . A method according to  claim 1  wherein, the obtained digital image is a colour digital image, the method includes the step of the separating the colour digital image into each of its component parts to produce three separate gray-scale digital images. 
   
   
       13 . A method according to  claim 12  including the step of measuring for the test area of each of the component part gray-scale digital images the average pixel luminance value and the standard deviation of the luminance values for all of the pixels in the test area. 
   
   
       14 . A method according to  claim 13  including the subsequent step of selecting for further analysis the component part gray-scale digital image with the largest pixel luminance standard deviation. 
   
   
       15 . A method according to  claim 12  wherein the Blue light component part gray-scale digital image is not used for further analysis if the substrate contains a brightening agent. 
   
   
       16 . A method according to  claim 10  including the step of enhancing the gray-scale digital image. 
   
   
       17 . A method according to  claim 16  wherein the luminance value for each pixel within the test area of the gray-scale digital image is adjusted if the luminance value of that pixel differs from an average luminance value for all of the pixels within the test area of the gray-scale digital image. 
   
   
       18 . A method according to  claim 17  wherein the enhancement includes adjusting the luminance value of each pixel within the test are by a multiplying factor. 
   
   
       19 . A method according to  claim 18  wherein the multiplying factor is determined by the arithmetic distance of the luminance value of each pixel from the mean pixel luminance value of all of the pixels in the test area. 
   
   
       20 . A method according to  claim 16  including the step of adjusting the luminance value for each pixel in the test area so as to spread the pixel luminance values of all of the pixels in the test area substantially evenly throughout the visible range. 
   
   
       21 . A method according to  claim 16  including the step of providing on a viewable output a digital display of the enhanced gray-scale digital image. 
   
   
       22 . A method according to any preceding claim including the step of providing a viewable output indicative of the quality of the printed image. 
   
   
       23 . An image obtaining apparatus, the apparatus including: —
 a device to obtain a digital image of a portion of a surface of a substrate;   a storage device to store information relating to the obtained digital image; and   a device to measure one or more physical characteristics of the obtained digital image so as to provide information indicative of the quality of the substrate, wherein the apparatus also includes a light source for illuminating the portion of the surface of the substrate, so as to cast shadows over the surface of the substrate at or near regions of the surface of the substrate which are uneven.   
   
   
       24 . (canceled) 
   
   
       25 . (canceled) 
   
   
       26 . (canceled) 
   
   
       27 . (canceled)